As background for our invention, circuit cards and devices have been protected from environmental effects by polymeric encapsulation, metal covers, hermetically sealed metal or ceramic covers and combinations of the aforementioned techniques. The encapsulation or potting methods provide conformal coating but the coating does not provide a hermetic barrier to moisture permeation or chemical diffusion. It also does not provide reliable EMI/ESD protection for the underlying hardware. Standard formed or machined metal covers or dust covers are only mechanically fastened over the assembly and do not provide environmental protection or complete EMI protection.
Hermetically sealed covers of ceramic or metal do provide environmental protection but tend to be bulky, heavy and expensive. Both cover methods, do not insure EMI/ESD protection, depending upon the configuration. The metal covers also tend to add unwanted dimension and weight to the assembly.
Furthermore, use of electrostatic discharge (ESD) bags and ESD bag material for a cover work in protection of underlying hardware from mild electrical effects but does not provide the hermetic environmental protection. The polymeric bags are suseptible to chemical diffusion and moisture permeation. Numerous ESD bags are available on the market, but none provide satisfactory results. The ESD bags have metallized layers that are too thin to prevent permeation or diffusion of external media through the metal layer.
However, new and existing film metallization processes, such as magnetron sputtering and roll plating, along with development of high performance polymer films are allowing for the feasible design of light weight, formable and hermetic metallized polymer film covers to replace or enhance the above techniques for protection of electronic devices and assemblies.